package com.liuhaoqi.raletiveblog;

import java.util.Scanner;

/**
 * @Author liuhaoqi
 * @Date 2020/8/6 19:46
 * @Version 1.0
 */
public class test {
    public static void main(String[] args) {
        double s = 0;
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();

        for (int i = 1; i <= 2*n; i++){
            if (i % 2 == 0) {
                s -= 1.0 / i;
            } else {
                s += 1.0 / i;
            }
        }
        s=s/5;
        System.out.printf("%.4f", s);
    }

}
